Marking pens such as fluorescent markers serve primarily for highlighting of specific sections of interest. Thus, the coloring property of a marking pen is an important characteristic for increasing the visibility of writing lines and making target locations stand out. However, marking pens with excellent coloring properties have had a problem in that drawn writing lines have been undesirably visible from the back sides of the papers (show-through). This problem of show-through is notable when writing on thin papers of dictionaries and the like, or papers that have low density and are highly permeable to ink. Examples of marking pens designed to reduce show-through include marking pens using the water-based ink compositions described in Japanese Unexamined Patent Application Publication No. 2010-150331 and Japanese Unexamined Patent Application Publication No. 2006-206640. However, marking pens that are resistant to show-through usually have limited ink discharge, and their coloring properties are also limited. Thus, such marking pens tend to be insufficient in terms of either or both reduced show-through and coloring properties.
Solid fluorescent markers are also known that comprise solid inks with increased ink viscosity. However, while solid fluorescent markers are resistant to show-through, they have poor coloring properties compared to fluorescent markers using liquid inks, and are also associated with problems such as difficult marking at target locations and high variation in line widths because of the crayon-like writing mechanism, such that the original function of the fluorescent marker cannot be satisfactorily exhibited.